1. Field of the Invention
This invention relates to tools used to sample fluids from a formation reservoir in a well, and more particularly, to a perforate, test and sample tool attached to the end of a tool string and having perforating guns, one or two packers, and a sampler above the packers adapted for entrapping a fluid sample without flowing well fluids into the tool string.
2. Description of the Prior Art
It is frequently necessary to obtain information about well fluid in a well formation reservoir prior to actually producing the well. Measuring the pressure and temperatures of the fluid is important, but it is also desirable to obtain an actual sample of the fluid and bring that sample to the surface so that the physical characteristics of the fluid may be observed. As a result, numerous testing and sampling apparatus have been developed.
One such formation tester is disclosed in U.S. Pat. No. 2,169,559 to Halliburton, assigned to the assignee of the present invention. This apparatus includes a packer with perforating guns positioned therebelow and having a valve therein such that after the packer is set and the guns triggered, fluid from the well formation reservoir flows through the valve into a cylindrical body at the lower end of the tool string. The valve is reclosed such that a volume of fluid is contained in the lower portion of the tool string. The tool string may be removed from the well bore and the sample drained for testing.
One problem with this apparatus and other sampling apparatus previously known is that hydrocarbons from the well formation are actually flowed into the tool string or to the surface. Because the formation is at a relatively high pressure, there is always the danger of a blowout of the well. Also, if sour gas is present in the sample fluid, special equipment is necessary on the surface and downhole for handling it.
One device which solves these problems by providing a tool with a totally enclosed sampling chamber is disclosed in U.S. patent application Ser. No. 064,285 to Christensen, assigned to the assignee of the present invention, and incorporated herein by reference. In this tool, the sampling chamber is configured such that the hydrocarbons from the well formation reservoir are never flowed into the tool string, and because the fluid sample is totally enclosed, the sampler may be handled at the surface. A minimum of special equipment is needed for handling the fluids in the sampler even if the sample fluid contains sour gas.
This previous apparatus using an enclosed sampling chamber has length limitations in the sampling chamber because it is positioned below the packer. The present invention is a variation on this previous device in which the sampling chamber is positioned above the packer or packers.
Other samplers adapted for obtaining a self-contained sample have been used on wirelines. In such apparatus, the tool is lowered on a wireline and perforating guns triggered and the sample chamber filled. Because the device is on a wireline, it is not possible for a large fluid sample to be obtained. The present invention which is lowered on a tool string obviously has no such weight limitations. Also, wireline sampling devices are not totally reliable and frequently the sample obtained is less than desirable.